Research

My group works on high-precision GPS applications, mostly for geoscientists. I began using GPS to measure crustal deformation in southern California. After I received my PhD, I continued working on plate boundary deformation, but also started thinking about measuring global effects with GPS: plate tectonics, effects of ice mass changes, and glacial isostatic adjustment. In the late 1990s and early 2000s, I moved on to bigger signals: moving ice sheets, volcanoes, and earthquakes. All of these signals required that we develop new ways of analyzing GPS data. While I am no longer active in this field, I did analyze data from some of the recent large earthquakes for fun. There was also a several year diversion into timing and relativity effects where I worked with professors in the Department of Physics and researchers at NIST. For many years I also worked on episodic slip and tremor in Guerrero, Mexico with UNAM. Almost ten years ago I began trying to model and remove multipath effects, mostly to improve GPS records of seismic displacements. It was that effort that led to my current research effort on GPS reflections. We use these reflections to study near-surface soil moisture, vegetation, and snow depth. A special effort focuses on developing water cycle products from EarthScope data: PBO H2O.